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1  Forum 2005-2010 (read only) / Development / Re: changing SCL and SDA pins of wire library on: September 19, 2009, 11:10:26 pm
Sorry for the bump, but I'm in a similar positoin.

I want to use all the analog pins for analog devices, however I also want to connect a I2C device.

I am going to try writing my own software implementation tomorrow, but has anyone got any recommendations about how I can run I2C on any IO pin?

2  Forum 2005-2010 (read only) / Development / Freeduino and Shields on: April 08, 2008, 11:13:00 pm

I own a Freeduino Diecimila compatible board. I was wondering if i purchase a standard Arduino shield, do the pins line up or has the Freeduino got slightly different pin positions? (due to its through-hole design...)

3  Forum 2005-2010 (read only) / Interfacing / Re: Interfacing 3.3V Arduino Pro with Servos? on: June 07, 2009, 08:17:00 pm
Power wasn't a huge issue I suppose, but can I use a 3.3V Arduino to actually communicate with the servo or do I need some kind of logic converter?
4  Forum 2005-2010 (read only) / Interfacing / Interfacing 3.3V Arduino Pro with Servos? on: June 06, 2009, 11:00:27 pm

I have a Arduino Pro 3.3V version. I was wondering how I would be able to interface this with standard 5V servos? Can this be done?

5  Forum 2005-2010 (read only) / Interfacing / Re: using Arduino to control mp3 decoder chip on: April 06, 2008, 05:31:20 am
You can easily find a PIC Programmer for under $400. Buy a ICD2 (Microchips flagship) clone off eBay for under $60 and will operate in MPLAB as a genuine ICD2 and you'll be set with one of the best programmers you can buy. Alternatively, for a bit of fun you could build your own:

If the software is already there, i would go with the PIC option.
6  Forum 2005-2010 (read only) / Interfacing / Re: Turning "on" a device which already has power on: January 05, 2008, 02:40:34 am
An optocoupler is no more than a LED and phototransistor in a dark box. When the LED is lit, the phototransistor fires up. The reason they are used is the two circuits are not electrically connected, where they are in standard transistors, protecting it from power surges. I would have thought a transistor would have been easier and i would have figured only to use an optocoupler only for special applications where its protection is needed, but hey, i guess it works.
7  Forum 2005-2010 (read only) / Interfacing / Re: LED Cubes and Current management? on: January 05, 2008, 01:50:18 am
One way is with an LED shift register driver chip like this:

That one has 16 bits, a search on google may turn up an 8 nit one at a lower price

Yes mem, i have seen the 16 bit LED Drivers, i was looking at the STP16C596, but that Texas Instruments one looks much the same. (I have even seen 32 bit ones) Are you saying that with 4 of thoes drivers, and a standard shift register on the other end, it will work no problem? That would be great, but from what i have seen is that shift register at the end cant handle potentially the current of 64 lit LEDs.
Offtopic: big93, about the LED Matrix. I am at work, but later on sure i can send my source. The basic idea is you start at row 1, and light all the columns you want lit on row 1, while sinking the row 1 pin, so only the first row is lit. Then do the same for row 2, 3, 4 and all the way to 7, and then do it all again. If you do it fast enough, using an effect called persistence of vision, your eyes will see it as them all lit up. (kind of how a CRT works) So just light a row at a time, really fast, and it will look like every LED is individually addressed.
A very good tutorial on the fundamentals of LED matrices is: (no code)
This blog post shows how someone built a Arduino based matrix:
Edit: - Thats exactly what you want. 7x5 scroller.
8  Forum 2005-2010 (read only) / Interfacing / LED Cubes and Current management? on: January 05, 2008, 01:22:13 am

I have mastered a 8x8 LED matrix using two shift registers, and now i want to add another dimension to it. I have thought long and hard about it and have done a fair amount of research. I plan to make a 64x8 array. The illustration below I made a while ago, but helps understand what im thinking.

This design will use 9 shift registers, 8 to make the 64 columns, and 1 to make the 8 rows. This is based off the advice given to me from someone else who had successfully used this design.

However, it's not the design that puzzles me, but how i mange the current to stay within the limits of the ICs and the LEDs. I don't understand what i have to put between the shift registers and LEDs. I understand the need for 220-ohm resistors, but i have read in some places i need transistors to take the large load of the ICs when dealing with matrices the size of mine. I have seen a few different ways, from simply having lots of transistors to a 'Darlington Transistor Arrays' or LED Drivers. Futhermore, Hypnocube, a commercial 4x4x4 tri-colour cube, clearly doesnt have a resistor on every LED, which i thought was a requirement.

I have found no definitive answer for what i place between the Shift Registers and the matrix, and with my lack of experience, i have just got confused. Does anyone know how i should manage the currents as to not blow the ICs or LEDs? (And idealy, save me the need to solder 64 transitors and/or resistors, as done in the Hypnocube)

Kind Regards,
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